Direct proof of use
The P-3C Orion is directly documented in the 2003 Iraq War through U.S. Air Forces Central reporting from Southwest Asia. In June 2009, AFCENT reported that Patrol Squadron EIGHT flew P-3C missions in support of Operation Iraqi Freedom, providing over-watch and indications-and-warning for coalition ground forces and collecting battlefield intelligence.
The same report described the aircraft's local role as primarily intelligence, surveillance, and reconnaissance, with electro-optical/infrared sensors, radar usable over land and sea, and satellite communications used to relay information to task-force commanders.
Sources: AFCENT P-3C Orion Watches Over Land and Sea
Timeline
Patrol and Reconnaissance Wing 11's public command history says that during Operation Iraqi Freedom, VP-45 became the first East Coast patrol squadron to establish a permanent detachment site in Iraq and flew combat missions in direct support of troops on the ground.
By June 2009, AFCENT reporting placed VP-8 P-3C aircraft in Southwest Asia supporting Operation Iraqi Freedom. The deployed squadron was flying slightly more missions for Operation Iraqi Freedom than for maritime security, while also patrolling the Arabian Gulf, Gulf of Oman, and Arabian Sea.
Sources: Patrol and Reconnaissance Wing 11 Command History, AFCENT P-3C Orion Watches Over Land and Sea
Role in the conflict
In the Iraq War record, the documented user was the United States Navy. The P-3C's role was not limited to maritime patrol: public U.S. military reporting describes its Iraq missions as overland surveillance, indications-and-warning for coalition ground forces, intelligence collection against battlefield forces, and communications relay to commanders.
The aircraft also retained a maritime-security role around the approaches to Iraq and the wider U.S. Central Command area. AFCENT described P-3C missions protecting U.S. maritime interests in the Arabian Gulf, Gulf of Oman, and Arabian Sea, while the Operation Iraqi Freedom sorties centered on coalition ground-force support and surveillance over Iraq.
Sources: AFCENT P-3C Orion Watches Over Land and Sea, Patrol and Reconnaissance Wing 11 Command History